Issue with outgoing/incoming calls

I have a 1+1 with 16.04 installed. In Canada with Rogers everything works fine. I'm back in Lebanon for a month, and bought a sim from MTC Touch. Everything works except incoming and outgoing calls. Attempts to recharge give a Invalid USSD Error. I've recovered and cleared the cache multiple times, I can set the carrier fine, to no avail. I'm wondering if there is any way to diagnose better the problem? The sim works fine from android and iphones. Any help is greatly appreciated.

I hope someone who knows more about the guts of cellular will chime in. I know next to nothing (very much not an expert), so please take the following with a grain of salt.

The only times I've heard of errors like this which persisted through reboots, it has been with older Android firmware, and the only times I've heard of it being fixed were with newer firmware. My presumption - which may well be faulty - is that the fix involved radio updates.

Therefore the only remedy I can think of would apply only if you hadn't updated to the latest OnePlus One firmware prior to flashing Ubuntu Touch. If so, you could presumably flash the last OxygenOS version OnePlus released for the One - or perhaps flash only the radio if that's possible - then test with Ubuntu Touch again and cross your fingers that it worked.

Obviously this would be pointless if you had been on the latest OxygenOS. It would also be time consuming, invasive, and drastic and would involve backing up and (unless you were able to flash only the radio) restoring your data.

It could be that I am entirely wrong about how USSD works or what Android partitions are completely overwritten by Ubuntu Touch and that the above is effectively nonsense, so I'd not recommend trying it unless you have a lot of time on your hands and are certain you have nothing to lose and have a good backup of your data. An easier route might be to buy a cheap Android or old Iphone to use for a month.

I very much hope someone else knows of an easier diagnostic or remedy or has some knowledge of USSD in UT.